Behavioural Ecology of Western Lowland Gorillas in Gabon

Abstract

The behavioural dogy of westem lowland goribs was studied for 16 months in the Lope Reserve, Ghn, where gdIw are sympatric with chimpttnaees in lowland tropicd fonst. Data were colle&d by dire& observation, and by examination of nesbdtes, feeding-sites, and trails. The nature of fmgivory and the extent of ~swal etion in food selection were emphasised. Dietary composition was identified, and the contribution offhitss was evaluated from the vohune of fruit ingest eatimated retrospeetiveIy from seeds in the gorillas' dung. Forest stmcture and emuposition were assessed using kansects, and Mt and leaf production wm quantified monthly tb estimate food availability. Food disttibution was patchy, and many faads showed seasonal peaks in adunhce. The heterogeneity of the habitat was reflected in the diverse diet: gorillas ate 139 park of 103 species of plants, including 78 fruits. One third of dung samples ~ontained weaver ants. Vegetative parts of Aframomum and Marantaceae formed staple foods, due to their abundance, accessibility, and year-round availabiE&. Succulent fruit formed over 905% of fruit intake. Seasonal variation waa memured in all dietary parameters. Flexible foraging strategies enabled gorilIadi to cope with fruit scarcity, particularly during the mGor dxy season: when less Wt wa8 available gorilla8 consumed more stems, leaves, and bark, and ate poorer-quality fibrous fnrits. Ranging was influenced by the seasrrnd avaiIabiIity of particular food species: when fruit was abundant gaxillas travelled large distances between sources, when scarce they adophd a lokoat stratew, shifting their diet to wards more abundazlt, but poorer quality foods, and travelling less. Differences in feeding, ranging, and climbing between lowland and mountain gorillas result hm striking differences in their respective habitats, especially in the abundance and distribution of fruit sources. Lowland gorillas' home ranges were larger; they spent more time in tress, mostly feeding; yet their social structure seemed to be similar to mountain gorillad. Lope gorillas adopted stratefies similar ta those of other ~~~VOMUS primates: fruib were preferred foods, consumed with fibre md leaves to meet nutritional requirements. The switch in diet was faciliated by the @XIast large body-size, which may have enabled them to cope wikh aucculent fruit shortages, and allowed garill~ts to remain in relatively etable groups.